Educational apparatus



1,636,234 P. E. KLOPSTEG EDUCATI ONAL APPARATUS Filed May 6, 1926 Jul 19, 1927.

, Patented July 19, 19 27.

PAUL E. KLOPSTEG, OF CI-IICAGO, ILLINOIS, ASSIGNOR TO CENTRAL" SCIENTIFIG COIL- PANY F- CHICAGO, ILLINOIS,

A CORPORATION OF ILLINOIS.

EDUCATIONAL APPARATUS.

Application filed May 6,

The principal object of this invention is to produce apparatus for measuring the velocity of'a projectile, and for illustrating Newtons second law of motion, and the conservation of momentum by means so simple thatbeginners can successfully use it and yet involving principles so fundamental as to intrigue/the interests of advanced investigators. g V

.More specifically, itis the object of the invention to combine a ballistic pendulum with a projectile impeller and a stop mechanism' tliat'will permit the investigator to first subject the pendulumto the action of the pro jectile" and'holdit in its biased or deflected position while the proper measurements are made, and later permit" the projectile to be thrown free of the pendulum to trace its trajectory to a selected 'level whereby the determinations canbe checked accurately and scientifi cally;

. Further objects and advantages of the in vention will become apparent as the disclo sure proceeds and the description is read in connection with the accompanying drawings illustrating'a selectedembodiment of the in vention, a nd in which 1" is a side elevation of the preferred fornr ofapparatus, the propeller mechanism 80 being shown invertical sectionand the bob being shown innormal position in solid lines andin deflected position in dotted lines;

Fig. 2iis an enlarged section through the bob taken. in the plane of the paper in Fig. 1;

Fig; 3 is a vertical section of'a fragment taken on the li'ne 83 of Fig. 1;

Figi is a vertical section of a fragment taken on'the li nel-Aof'Fig. 1, and

Fig; 5' is a side'elevation similar to Fig. 1, indicating the use of apparatus in determining the time'of flight'of a projectile.

The preferred form ofiapparatus here il lustrated is groupedupon a heavy cast iron base 10, having legs 11, equipped 'with rub ber-Ifeet 12, to protect the top of the table 13 (Fig. 5) or other furniture upoirwh-ich the apparatus may be placed.

Adjacent-to one side and between the ends ofthe'base' anupright mast 1 1 is erected the upper end 'of'which is equipped with a boom orhead. 15 consisting'of a hollow boss 16 (Fig; 3) receiving the mast and a laterally sition of that character.

1926. Sean 107,2i'3.

projecting arm 17 having spaced downwardly projecting lugs 18 equipped with adjustable pivotflbearings 19 and 20.

A massive bob 21 is fixed to the lower end of a light red 22 which'has an enlargement 1 this bore enlarged as indicated at 27 to receive the outer edge of a cushion 28 formed of ordinary steam packing, or other compo- Beyondthe steam packing thebore is reduced to a finger'hole 29 to admit a? finger to eject the ball 30 The ball is held inthe bore 26 by a spring 31'' secured to the bob at 82, bending downwardly and then upwardly, as indicated at 33, whereby it willreadirly admit the ball and then retain it in position to continue the center of gravity of the suspended mass in line with the axis of the rod 22.

. On the front side of the bob is an indicator 34: adjustably mounted in a slot by the screw and'having a point-36 to be set opposite to the center of gravity of the suspended inass.

Adjacent to the right of the base 10 is a propeller frame '3'? having a flanged foot 38 secured to the base 10 and projecting at 89 to the right beyond the base 10, where it terminates in a downwardly inclined pistolgrip 40. On the upper side of the frame 37 at each end are spaced bosses 41 and 42" bored in alignment with the axis of the bore 26 of the bob 21. A propelling rod 13 is moun'tedto move on these bores and is reduced at 4% to enter a hole 4t5inthe ball 30 which serves as a projectile "in the use of the apparatus. Thebore of the' boss 42 is larger than the rod and receives a threaded sleeve 46 having a knurled flange 47. Between the sleeve and "a collar 18 on'the rod a helical spring L9 is coiled. and the ne end of the rod is atapered col lar 5O terminating in a shoulder 51 adapted to cooperate with the catch 52 on a'trigger 53 fulcrumed a -J54 on'the portion 39 of the Between the collar 48 frame 37 and bent downwardly to form the finger arm 55, lying partly in front and partly in a slot in the pistol-grip 40.

On the end of the base 10 opposite to the propelling device and adjacent to one side, a short mast or post 56 is erected out of alignment with the bob 21. A bracket 57 mounted on this post projects laterally and supports a graduated rack 58 in alignment with the hob and adapted to be engaged by a pawl 59, pivoted on the pin 60 extending across the slotted bottom 61 of the bob. The engaging end of the pawl is sharpened, as indicated at 62, and normally sets in position to positively engage the rack. A pin 63 adjacent to the engaging end of the pawl cooperates with the one end of a light positive spring 64.- which is wound about the pin 0 and has its opposite end 65 resting against the bob at the base 66 of the slotted portion. The pawl is made very light and the spring is so designed that the engagement of the pawl with the rack, while the pendulum is swinging outwardly, results in a very small amount of resistance, but the pawl quickly and positively engages the rack upon a cessation of outward movement and serves to re tain the pendulum at or very close to the imit of its outward movement.

The rack 58 is curved on an arc whose center lies in the axis of the pivot bearings 19 and 20, or the axis about which the pendulum swings. It is graduated and preferably numbered every five notches.

Theory.

Measurement of velocity by a ballistic pendulum is based on the principle of con- "ervation of momentum, the latter being delined as the product of mass and velocity of a moving body. The fundamental principle of conservation of momentum is that the momentum of the two masses is the same before and after impact.

here a projectile is embedded in a pen duluiu the velocity before impact is zero and after impact according to Newtons second law of motion the common velocity of the pendulum bob and the projectile must be such that the momentum of the combined masses is equal to the momentum of the projectile before impact. This relation may be indicated by the following equation written. in two ways:

where M is the mass of the pendulum, m the mass of the projectile, V the velocity of the pendulum and projectile immediately after impact, 4) the velocity of the projectile before impact.

The impact causes the pendulum to swing and its center of gravity rise a distance h,

the kinetic energy at impact must equal the potential energy when the pendulum reaches its highest point. This relation may be written as follows:

V J2gh (Eq. 3.) By measuring the height it, weighing the masses M and m and substituting these values in Equation 2, V may be ascertained, then substituting M, m andV in Equation 1 will give the value of o. 7

The results thus obtained may be checked by data obtained from the flight of the roject-ile independent of the pendulum. uring the time interval 6, the projectile will move horizontally through a distance D='vt, and during the same interval under the force of gravity it will fall a distance d gt (Eq/l).

Suppose the projectile, after a flight of t seconds, strikes a horizontal plane at a distance (5 below its initial position. If the point where it struck and its initial position areknown, the horizontal and vertical distances between these points respectively are the values of D and (Z in Equations 3 and 4. By eliminating t and substituting the measured values of D and (Z, c is found to be From Equation 4, t, the time of flight can be found.

In the first part of the experiment the ball 30 is placed on the end 44 of the rod 43 and together they are pressed to the right in Fig. 1 until the trigger catches the collar 50. The bob is set at rest in the solid line position in Fig. 1, the trigger is pulled, the projectile is thrown to the left taking the position within the bob shown in Fig. 2 and swinging the bob to the dotted line position shown in Fig. 1. This should be repeated several times and the position of the point of the ball 62 noted. The average will accurately represent the mean height to which the center of gravity of'the combined masses has swung. Measuring h and k and subtracting will give it for use in Equation 3.

For the second part of the experiment swlng the bob to the position shown in Fig. 1 and, after setting the propelling device, pull the trigger and permit the ball to trace the trajectory 70 as indicated in Fig. 5. Perform this several times and note the given distance, then measure (Z and D for use in Equation 5.

The pivot bearing 20 is provided with a knurled head 71 which may be readil screwed in and out of the flange 18 and :1 jacent to the head it has a shoulder 72 adapted to contact with the flange when the bearings are in proper adjustment. The

pivot bearing 19 is provided with a screw driver slot 73, or the like, by which the initial adjustment can be made. The space between the flanges 18 receives the enlargement 23 with sufficient clearance to permit the latter to be removed when the pivot bearing 19 alone has been withdrawn. This construction enables the student to replace the pendulum after weighing, and set the hearings in proper adjustment by merely screwing up the pivot bearin g 20.

The mast let is cylindrical and its lower end is received in a cylindrical bore 74 in the base 10. One wall of this bore is equipped with a screw 75 having a conical point 76 and the mast has a conical socket 77 to cooperate with the point. This construction permits the mast to be removed for shipment, or storage, and replaced in proper adjustment by merely inserting it in the socket and setting up the screw 75.

I claim as my invention:

1. In apparatus of the class described, a ballistic pendulum including a' massive bob suspended by a light rod having opposed tapered bearing sockets, a support, adjustable pivot bearings carried by the support and cooperating with the tapered bearing sockets, and a stop for limiting the adjustment of one of said pivot bearings.

2. In apparatusof the class described, a ballistic pendulum including amassive bob suspended by a light rod having opposed tapered bearing sockets, a support receiving the rod with clearance, pivot bearings threaded in the support and having tapered ends cooperating with the tapered bearlng sockets, and a shoulder on one of said pivot' bearings adapted to bear against the support when the bearings are properly adjusted.

3. In apparatus of the class described, the combination'of-a ballistic pendulum including a massive bob suspended by a light rod, an impeller for directing a projectile against the bob, a bracket out of line with the pendulum, a rack carried by the bracket in line with the pendulum at an angle to its posi-- whose center is the axis of suspension of the pendulum, and a light spring-pressed pawl carrlliied by the bob in position to engage the rac 5. In apparatus of the class described, the combination'of a ballistic pendulum including a bob and asuspending rod, a pro jectile, and a propeller including a fralm having spaced bores aligned with the bob, an impelling rod mounted in the bores and projecting toward the bob to receive the proectile, a spring urging the rod toward the bob, a collar onthe rod between the bores, and a trigger mounted on the frame and cooperating with'the collar.

6. In apparatus of the class described, the combination of a ballistic pendulum including a bob and a suspending rod, a projectile and a propeller including a frame having spaced bores aligned with the bob, an impelling rod mounted in the bores and projecting toward the bob to receivethe projectile, a spring urging the rod toward the bob, means for adjusting the ressure of the spring, and a trigger pivote on. the frame and releasably engaging the rod. 7

7. In apparatus of the class described, the combination of a basehaving a socket, a ballistic pendulum includinga mast having one end mounted in the socket and provided with a conical recess and a set screw mounted in the base and having a conical point for cooperation with the recess.

8. In apparatus of the class described, a. ballistic pendulum including a bob having a bore extending from one side to the opposite side, a cushion secured in the bottom of the bore and a spring projecting into the I bore for holding a projectile against the cushion.

9. In apparatus of the class described, the combination of a heavy base having a substantially horizontal top, a ballistic pendulum including a bob suspended by a light rod, a mast mounted at one side of the base between the ends and carrying a support in which the light rod is pivotally mounted on an axis transverse to the base, a propeller mounted at one end of the base and having a propelling rod in alignment with the bob when it is in a position of rest, a support adjacent to the opposite end of the base out of line with the bob, a rack carried by the support in line with the bob and a pawl car-- rie(1l{ by the bob for engagement with the rac In testimony whereof I afiix my signature. PAUL E. KLOPSTEGT 

